Process for the hydroxycarbonylation of pentenoic acids

ABSTRACT

The present invention relates to a process for the hydroxycarbonylation of pentenoic acids. By the process, one or a number of pentenoic acids are hydroxycarbonylated to adipic acid, by carbon monoxide and water, in the presence of a catalyst based on iridium and/or rhodium and of at least one iodinated promoter. The reaction mixture obtained is subjected to a refining operation, after having optionally been concentrated, making it possible to separate at least a part of the catalyst. The catalyst thus separated is recycled to an operation for the hydroxycarbonylation of pentenoic acids, of butadiene, or of butadiene derivatives.

This application was filed on Oct. 19, 1993 as International ApplicationNo. PCT/FR93/01028.

The present invention relates to a process for the hydroxycarbonylationof pentenoic acids for the preparation of adipic acid, in the presenceof a catalyst which is at least partly separated from the reactionmixture obtained after the hydroxycarbonylation and reused in ahydroxycarbonylation operation.

One of the most promising processes for the preparation of adipic acidconsists in hydroxycarbonylating one or a number of pentenoic acids,especially 3-pentenoic acid and 4-pentenoic acid, using carbon monoxideand water, in the presence of a catalyst based on iridium, rhodium ortheir mixtures and of an iodinated promoter. Generally, the reaction iscarried out in the liquid phase at a temperature from 50° C. to 300° C.and under a partial carbon monoxide pressure of a few bar. In order toenvisage the industrial use of a process of this type, it is veryobviously indispensable to be able to recycle at least part of theexpensive catalyst used.

The subject of the present invention is specifically a processcontaining such a recycling.

Among the separation techniques which can be envisaged, distillation ofthe more volatile compounds of the reaction mixture resulting from thehydroxycarbonylation allows the catalyst to remain with the diacidsformed. A subsequent distillation of these diacids at low vapourpressure makes it necessary to subject them, and the catalyst, to aprolonged heating at a relatively high temperature, capable of degradingthem and making the catalyst partially or entirely inactive.

The crystallization technique requires a sufficient heat transfer to beprovided and for the production of crystals of a requisite size to befiltered off to be possible. In addition, the maximum level of solids islimited to an upper value of the order of 30 to 40%. All this leads to asignificant equipment volume and to the immobilization of an excessivelylarge amount of very expensive catalyst.

The present invention proposes to solve the problem of the separationand recycling of the catalyst in the context of a process for thehydroxycarbonylation of pentenoic acids to adipic acid, by the use ofthe refining technique.

More particularly, the subject of the invention is a process for thehydroxycarbonylation of pentenoic acids, characterized in that:

one or a number of pentenoic acids are hydroxycarbonylated to adipicacid, by carbon monoxide and water, in the presence of a catalyst basedon iridium and/or rhodium and of at least one iodinated promoter,

the reaction mixture obtained is subjected to a refining operation,after having optionally been concentrated, making it possible toseparate at least a part of the catalyst,

the catalyst thus separated is recycled to an operation for thehydroxycarbonylation of pentenoic acids or of butadiene or of butadienederivatives.

Pentenoic acid is understood to mean, in the context of the invention,2-pentenoic acid, 3-pentenoic acid, 4-pentenoic acid and their mixtures.

3-Pentenoic acid, taken in isolation or as a mixture with its isomers,is more particularly suitable, owing to its accessability and thesatisfactory results to which it leads during its hydroxycarbonylation.

The catalyst used for the hydroxycarbonylation reaction can be based onrhodium, iridium or both these metals.

Any rhodium or iridium source is capable of being used.

Reference may be made, as examples of rhodium sources which canespecially be used, to the compounds mentioned in European PatentEP-A-0,477,112, the contents of which are incorporated for reference inthe present Patent Application.

Mention may be made, as examples of iridium sources which can especiallybe used, of:

metallic Ir, IrO₂, Ir₂ O₃,

IrCl₃, IrCl₃.3H₂ O,

IrBr₃, IrBr₃.3H₂ O,

IrI₃,

Ir₂ (CO)₄ Cl₂, Ir₂ (CO)₄ I₂,

Ir₂ (CO)₈, Ir₄ (CO)₁₂,

Ir(CO)[P(C₆ H₅)₃ ]₂ I,

Ir(CO)[P(C₆ H₅)₃ ]₂ Cl,

Ir[P(C₆ H₅)₃ ]₃ I,

HIr[P(C₆ H₅)₃ ]₃ (CO),

Ir(acac)(CO)₂ ;

[IrCl(cod)]₂,

(cod=1,5-cyclooctadiene,

acac=acetylacetonate).

The iridium-based catalyst which are more particularly suitable are:[IrCl(cod)]₂, Ir₄ (CO)₁₂ and Ir(acac) (CO)₂.

The catalyst based on iridium or based on iridium and rhodium areparticularly preferred in the context of the process of the invention.

The amount of catalyst to be used can vary within wide limits.

In general, an amount expressed in moles of metallic iridium and/or ofmetallic rhodium per liter of reaction mixture between 10⁻⁴ and 10⁻¹leads to satisfactory results. Lower amounts can be used: however, it isobserved that the rate of reaction is low. Larger amounts havedisadvantages only at the economic level.

The iridium and/or rhodium concentration is preferably between 5·10⁻⁴and 10⁻² mol/liter.

Iodinated promoter is understood to mean, in the context of the processof the invention, HI and the organoiodinated compounds capable ofgenerating HI under the reaction conditions and more particularly thealkyl iodides having 1 to 10 carbon atoms. Methyl iodide is moreparticularly recommended.

The amount of iodinated promoter to be used is generally such that theI/Ir (and/or Rh) molar ratio is greater than or equal to 0.1 It is notdesirable that this ratio exceeds 20. The I/Ir (and/or Rh) molar ratiois preferably between 1 and 5.

The presence of water is indispensable to carrying out thehydroxycarbonylation. Generally, the amount of water to be used is suchthat the water/pentenoic acids molar ratio is between 0.01 and 10.

A larger amount is not desirable due to the loss in catalytic activityobserved. The water/pentenoic acids molar ratio in the reaction mixturecan be instantaneously less than the minimum value indicated above, ifthe reaction is carried out, for example, with continuous injection ofwater, rather than introducing it with the other charges before thehydroxycarbonylation reaction.

The water/pentenoic acids molar ratio is preferably between 0.01 and 1,the preceding comment regarding the minimum value also being valid.

The hydroxycarbonylation reaction can be carried out either in a thirdsolvent or in a large excess of pentenoic acids.

It is possible to use, as third solvent, especially the saturatedaliphatic or aromatic carboxylic acids containing at most 20 carbonatoms provided that they are liquid under the reaction conditions. Theremay be mentioned, as examples of such carboxylic acids, acetic acid,propionic acid, butyric acid, valeric acid, adipic acid, benzoic acidand phenylacetic acid.

The third solvent can also be chosen from saturated aliphatic orcycloaliphatic hydrocarbons and their chlorinated derivatives andaromatic hydrocarbons and their chlorinated derivatives, provided thatthese compounds are liquid under the reaction conditions. There may bementioned, as examples of such solvents, benzene, toluene,chlorobenzene, dichloromethane, hexane and cyclohexane.

When it is present in the reaction mixture, the third solventrepresents, for example, from 10% to 99% by volume with respect to thetotal volume of the said reaction mixture and preferably from 30% to 90%by volume.

According to a preferential variant, the hydroxycarbonylation reactionis carried out in the pentenoic acid themselves, that is to say2-pentenoic acid, 3-pentenoic acid, 4-pentenoic acid and their mixtures.

The hydroxycarbonylation reaction is carried out at a pressure greaterthan atmospheric pressure and in the presence of carbon monoxide. It ispossible to use essentially pure carbon monoxide or carbon monoxide oftechnical quality as it is found in commerce.

The reaction is carried out in the liquid phase. The temperature isgenerally between 100° C. and 240° C. and preferably between 160° C. and200° C.

The total pressure can vary within wide limits. The carbon monoxidepartial pressure, measured at 25° C., is generally from 0.5 bar to 50bar and preferably from 1 bar to 25 bar.

The reaction mixture emerging from the hydroxycarbonylation reactionessentially contains the unreacted pentenoic acids, water, the iodinatedpromoter, the catalyst, the solvent optionally used, the adipic acidobtained, and the other by-products formed in more or less significantamounts, such as, for example, 2-methylglutaric acid, 2-ethylsuccinicacid, valeric acid or gamma-valerolactone (or 4-methylbutyrolactone).

This reaction mixture is subjected to a refining operation, either assuch or preferably after a concentration operation, consisting inremoving, especially by distillation, a part of or all the thirdsolvent, if such a solvent was used, or a part of the excess pentenoicacids when the reaction was carried out without a third solvent. By sucha concentration, the weight of the reaction mixture is generally reducedto a value representing from 10% to 90% of its initial weight, withoutthese figures having a critical value.

Refining in the present text is defined as the direct crystallization ofthe reaction mixture, preferably concentrated, on a cooled wall, onwhich the raffinate (essentially adipic acid) is deposited, whereas theremaining liquid is concentrated in the other constituents of thetreated mixture, including the catalyst. However, the crystal latticedeposited retains, by capillary attraction or inclusion, a limitedamount of the residual liquid.

This technique is also known under the name of molten mediumcrystallization.

In the context of the process of the invention, the main object of therefining is to separate the majority of the adipic acid from thecatalyst which remains essentially in the liquid residue (draw-off); forthis, an apparatus is chosen which has a high heat exchange surfacearea/volume of reaction mixture to be treated ratio, so as to limit theduration of crystallization of the raffinate and especially the time thereaction mixture spends in the refiner and makes possible a degree ofcrystallization which can exceed 70%.

The refining operation can be described in the following general way.

The reaction mixture to be treated is introduced into the apparatus atan initial temperature at least equal to the crystallization temperatureof the mixture and preferably between this temperature and thetemperature at which the hydroxycarbonylation reaction was carried out;the apparatus is itself also at this temperature.

This initial temperature is generally between 100° C. and 200° C.

The first phase of the operation consists in the progressivecrystallization of adipic acid on the walls of the apparatus. Thiscrystallization is obtained by a programmed reduction in the temperatureof the heat-exchange walls, especially using a heat-transfer fluidcirculating on the other side of the said walls.

Depending on the type of industrial production envisaged, thetemperature reduction can be more or less rapid, according to whetherthe mixture to be treated crystallizes in the relatively thin layer whenit does not fill the whole volume of the apparatus or whether itcrystallizes in forming a thick layer when the charged mixture isimmobile and fills the whole volume of the apparatus.

The final temperature achieved is limited by the melting temperature ofthe eutectic of the various constituents of the reaction mixtures. Itwill be chosen according to the composition of the reaction mixture tobe refined and according to the amount of adipic acid which it isdesired to crystallize. As a general rule, the lower this temperature,the more certain other constituents of the reaction mixture riskcontaminating the adipic acid crystals; conversely, the higher thistemperature, the lower will be the degree of recovery of adipic acid inthe raffinate.

Taking into account the above, the final temperature is generally fixedbetween 0° C. and 70° C.

When the final temperature chosen is achieved, the draining fraction,enriched in catalyst and impoverished in adipic acid with respect to thereaction mixture treated, is recovered by running from the lower part ofthe equipment. This constitutes the draining phase.

The third phase of the refining operation consists in washing thecrystals deposited on the walls of the equipment, so as to recover themajority of the drained liquid still retained on the said crystals. Itis carried out by reheating the deposited crystals, at a rate whichvaries depending on the type of industrial production, which causestheir partial melting; draining and replacement on the crystals of thedrained liquid by a liquid much richer in adipic acid is thus produced.This phase is called sweating phase. Its quantitative significancedepends on the amount of catalyst which it is desired to recover andconditions the purity and the degree of recovery of the adipic acid. Thesweating fraction can be added to the fraction obtained during thedraining phase or be subjected to another separation operation of itsconstituents by any technique, especially by refining.

The term draw-off denotes, in the present text, the part of the reactionmixture separated during the draining phase and/or the sweating phase.

The temperature to which the raffinate is brought during the sweatingphase varies depending on the amount of catalyst which it is desired torecover or the amount of purified adipic acid which it is desired toobtain.

This temperature is generally between the final temperature of thedraining phase and 150° C. It is preferably between 100° C. and 145° C.

The raffinate deposited on the walls of the equipment can then berecovered by rapid melting of the crystals.

The duration of the refining cycle, consisting of these various phases,can vary from approximately 1 hour to 30 hours, depending on theindustrial technology adopted; thus, a dynamic thin-layer system,offering a large heat exchange surface area with respect to the volumeto be treated, will require a much shorter duration than a staticthick-layer system.

The draw-off, containing at least a part of the catalyst, iodinatedpromoter, unconverted pentenoic acids and more or less significantamounts of the various constituents of the treated reaction mixture, canbe directly recycled to a hydroxycarbonylation reaction (especially thedraining fraction), or the subjected beforehand to one or a number ofseparation operations, targeting the separation of the catalyst from allor part of the other constituents (especially the sweating fraction).This additional separation can itself be carried out by the refiningtechnique; however, it can be carried out by any other conventionaltechnique such as, for example, crystallization, distillation,extraction.

The raffinate, largely containing adipic acid as well as the catalystand more or less significant amounts of the various constituents of thetreated reaction mixture, can be itself subjected to one or a number ofadditional separation operations, in order to separate the catalyst andthe iodinated promoter which it contains. As indicated above for thedraw-off, this additional separation can itself be carried out by therefining technique; however, it can be carried out by any otherconventional technique such as, for example, crystallization,distillation, extraction. The catalyst and the iodinated promoter thusseparated can then optionally be recycled.

The refining is carried out so that at least 40%, and preferably atleast 80%, of the catalyst present in the reaction mixture to be treatedis separated.

A preferential method of the invention consists in carrying out arefining operation, during which at least 80% of the catalyst isseparated, between an initial temperature between 100° C. and 200° C.and a final temperature for the draining phase between 20° C. and 60°C., the temperature then being raised to between 100° C. and 145° C. forthe sweating phase; this refining operation is optionally followed byone or a number of other separation operations carried out on some orall of the fractions obtained in order to separate the remainder of thecatalyst, on the one hand, and at least a part of the branched diacids,on the other hand. The catalyst thus obtained during the refining isrecycled to the hydroxycarbonylation reaction.

When the catalyst separated by the refining operation is used for thehydroxycarbonylation of butadiene or of its derivatives, there will beused, for example, the technique described for rhodium in PatentEP-A-0,405,433 and EP-A-0,274,076.

Besides butadiene, its derivatives which are the most generally usableare 3-buten-2-ol, 2-buten-1-ol, their mixtures and their carboxylicesters, especially the acetates, propionates, valerates, adipates andpentenoates.

The examples which follow illustrate the invention.

EXAMPLE 1 Hydroxycarbonylation of 3-Pentenoic Acid

The following are introduced into an autoclave equipped with stirring bya self-priming turbine:

2.45 g (7.3 mmol) of Ir in the form of [IrCl(cod)]₂ (3.3 mmol/l ofreaction mixture)

4.17 g (18.6 mmol) of HI in the form of a 57% in weight for weightaqueous solution (8.4 mmol/l)

177.8 g (9.9 mol) of water (4.5 mmol/l)

2084 g (20.84 mol) of 3-pentenoic acid (P3).

The autoclave, connected to the gas supply under pressure, ishermetically closed. 2 bar (0.2 MPa) of CO are admitted while cold andheating is carried out to 185° C. over 20 min via an electric bandheater. When this temperature is achieved, the pressure is adjusted to20 bar (2 MPa).

The kinetics of the reaction are monitored by the absorption of CO in areserve connected to the reactor, the pressure in the autoclaveremaining constant.

After a reaction duration of 30 min, corresponding to the completeconsumption of the introduced water, the reaction is halted by coolingthe reaction mixture. The autoclave is degassed and the reaction mixtureis drawn off in the liquid state at 120° C.

The reaction mixture is analysed by vapour phase chromatography and byhigh performance liquid chromatography.

    ______________________________________                                        degree of conversion (DC) of P3:                                                                    51%                                                       molar yield with respect to converted    65%                                  P3 (Yd.) of adipic acid (A1):                                                 Yd. of methylglutaric acid (A2):    11%                                       Yd. of ethylsuccinic acid (A3):       3%                                      Yd. of gamma-valerolactone (VAL):   11%                                       Yd. of valeric acid (Pa):            2%                                       Yd. of 2-pentenoic acid (P2):        8%                                     ______________________________________                                    

The degree of linearity, expressed by the ratio in percentage of A1formed to all the diacids A1, A2 and A3 formed, is 82%.

The rate of reaction (calculated over 20 min of absorption of CO) is 5.4mol of CO absorbed per hour and per liter of reaction mixture.

The reaction mixture is concentrated by distillation of the volatileproducts at 90° C. under a pressure of 1 kPa; a mixture is thus obtainedwhich is subjected to a refining operation.

EXAMPLE 2 Refining of the Concentrated Reaction Mixture Prepared inExample 1

The apparatus used consists of a metal cylinder, with an internaldiameter of 45 mm and a height of 65 cm, closed at its base by asmall-volume pneumatic valve and equipped at its top with a screw-on lidthrough which two temperature probes and a nitrogen inlet pass.

The assembly is surrounded by a double jacket making possible thearranged circulation of a heat-transfer fluid at a controlledtemperature.

1058 g of the concentrated reaction mixture prepared in Example 1, andwhich has the composition by weight given below, are used:

    ______________________________________                                        adipic acid            66.00%                                                   2-methylglutaric acid 11.20%                                                  2-ethylsuccinic acid 2.00%                                                    gamma-valerolactone 1.80%                                                     2-pentenoic acid 3.00%                                                        3-pentenoic acid 14.50%                                                       4-pentenoic acid 1.30%                                                        iridium (as a metal) 0.0887%                                                  iodine 0.1565%                                                              ______________________________________                                    

This reaction mixture, in the liquid state at 131° C., is charged to theapparatus which is at this same temperature.

The temperature is progressively lowered using the heat-transfer fluidto 40° C. over 9 hours: this is the crystallization phase.

At 40° C., the valve of the apparatus is opened and the draining phaseis carried out at a constant temperature for 3 h; the draining fraction,representing, in weight for weight, 20% of the reaction mixture charged,is thus recovered.

The temperature is then progressively raised to 138° C. over 11 h;during this sweating phase, a sweating fraction representing, in weightfor weight, 28% of the reaction mixture charged, is recovered.

Finally, the temperature is brought, over 3 hours, to the meltingtemperature of the raffinate deposited on the walls of the apparatus andis maintained at this temperature for a further one hour. The raffinateis thus recovered which represents, in weight for weight, 52% of thereaction mixture charged.

The respective compositions of these three fractions are determined byassaying by gas phase chromatography, by high performance liquidchromatography and by X-ray fluorescence.

    ______________________________________                                        Draining fraction:                                                              adipic acid 10.0%                                                             2-methylglutaric acid 32.0%                                                   2-ethylsuccinic acid 5.4%                                                     gamma-valerolactone 8.4%                                                      2-pentenoic acid 7.9%                                                         3-pentenoic acid 33.5%                                                        4-pentenoic acid 2.5%                                                         iridium (as a metal) 0.210%                                                   iodine 0.370%                                                                 Sweating fraction:                                                            adipic acid 48.0%                                                             2-methylglutaric acid 19.5%                                                   2-ethylsuccinic acid 3.3%                                                     gamma-valerolactone 4.8%                                                      2-pentenoic acid 5.5%                                                         3-pentenoic acid 18.5%                                                        4-pentenoic acid 0%                                                           iridium (as a metal) 0.133%                                                   iodine 0.228%                                                                 Raffinate:                                                                    adipic acid 95.8%                                                             2-methylglutaric acid 2.2%                                                    2-ethylsuccinic acid 0%                                                       gamma-valerolactone 0%                                                        2-pentenoic acid 0%                                                           3-pentenoic acid 2.0%                                                         4-pentenoic acid 0%                                                           iridium (as a metal) 0.0149%                                                  iodine 0.0264%                                                              ______________________________________                                    

The raffinate thus contains 76% of the adipic acid and only 9% of theiridium and the iodine present in the reaction mixture emerging from thehydroxycarbonylation reaction.

The draining fraction contains 45% of the iridium and of the iodine and3% of the adipic acid of the reaction mixture, whereas the sweatingfraction contains 46% of the iridium and of the iodine and 21% of theadipic acid. Overall, the draw-off consisting of the combined drainingand sweating fractions thus contains 91% of the iridium and of theiodine with 24% of the adipic acid of the reaction mixture. Differentdivisions of the fractions and raffinate make it possible either tominimize the amount of adipic acid present in the draw-off or toincrease the degree of recovery of the iridium and the iodine dependingon the favoured separation criterion.

EXAMPLE 3 Recycling of the Draining Fraction Obtained in Example 2 to aHydroxycarbonylation Reaction

100 g of the draining fraction obtained in Example 2 are recycled.3-Pentenoic acid and water are added to it so as to have an initialreaction mixture having the same concentration of Ir and of HI as theinitial mixture used in Example 1, that is to say 3.3 mmol/l of Ir and8.5 mmol/l of HI.

The concentrations in the initial mixture of the other constituents arethe following:

7 mmol/l of P3

0.2 mmol/l of P2

0.04 mmol/l of P4

0.24 mmol/l of VAL

0.18 mmol/l of A1

0.6 mmol/l of A2

0.1 mmol/l of A3

4.2 mmol/l of water.

The hydroxycarbonylation is carried out as described in Example 1. Afterreacting for 40 min, corresponding to the consumption of the introducedwater, the autoclave is cooled and the various constituents of the finalreaction mixture are assayed.

The following results are obtained:

    ______________________________________                                        degree of conversion (DC) of P3:                                                                    58%                                                       Yd. of adipic acid (A1):                65%                                   Yd. of methylglutaric acid (A2):    13%                                       Yd. of ethylsuccinic acid (A3):       3%                                      Yd. of gamma-valerolactone (VAL):    9%                                       Yd. of valeric acid (Pa):            3%                                       Yd. of 2-pentenoic acid (P2):        7%                                     ______________________________________                                    

The degree of linearity, expressed by the ratio in percentage of A1formed to all the diacids A1, A2 and A3 formed, is 80%.

The rate of reaction (calculated over 20 min of absorption of CO) is 4.4mol of CO absorbed per hour and per liter of reaction mixture. Thekinetics being of the order of 1 with respect to P3, the catalyst thushas an activity identical to that observed in Example 1 (absorptionvolume of CO/amount of P3 involved).

We claim:
 1. Process for the hydroxycarbonylation of pentenoic acids,wherein:one or a number of pentenoic acids are hydroxycarbonylated toadipic acid, by carbon monoxide and water, in the presence of a catalystbased on iridium and/or rhodium and of at least one iodinated promoter,the reaction mixture obtained is subjected to a refining operation,after having optionally been concentrated, making it possible toseparate at least a part of the catalyst, said refining operationcomprising direct crystallization of the reaction mixture on a cooledwall on which adipic acid is deposited while concentrating the catalystin the residual reaction mixture, the catalyst thus separated isrecycled to an operation for the hydroxycarbonylation of pentenoicacids.
 2. Process for the hydroxycarbonylation of pentenoic acids,wherein:one or a number of pentenoic acids are hydroxycarbonylated toadipic acid, by carbon monoxide and water, in the presence of a catalystbased on iridium and/or rhodium and of at least one iodinated promoter,the reaction mixture obtained is subjected to a refining operation,after having optionally been concentrated, making it possible toseparate at least a part of the catalyst, said refining operationcomprising direct crystallization of the reaction mixture on a cooledwall on which adipic acid is deposited while concentrating the catalystin the residual reaction mixture, the catalyst thus separated isrecycled to an operation for the hydroxycarbonylation of butadieneand/or of its derivatives.
 3. Process according to claim 1, wherein atleast 40% of the weight of the catalyst contained in the reactionmixture is separated by the refining operation.
 4. Process according toclaim 1, wherein the reaction mixture obtained after thehydroxycarbonylation operation is concentrated before being subjected tothe refining operation in order to eliminate at least a part of the morevolatile compounds which it contains.
 5. Process according to claim 4,wherein the concentrate of the reaction mixture subjected to therefining operation represents, in weight by weight, from 10% to 90% ofthe reaction mixture emerging from the hydroxycarbonylation operation.6. Process according to claim 1, wherein the hydroxycarbonylation iscarried out in a solvent selected from the group consisting of saturatedaliphatic or aromatic carboxylic acids having at most 20 carbon atoms,saturated aliphatic or cycloaliphatic hydrocarbons and their halogenatedderivatives, aromatic hydrocarbons and their halogenated derivatives andaliphatic, aromatic or mixed ethers.
 7. Process according to claim 1,wherein the hydroxycarbonylation is carried out in the pentenoic acidsthemselves.
 8. Process according to claim 1, wherein the refiningconsists in cooling the optionally concentrated reaction mixture in acontrolled and progressive way from an initial temperature at leastequal to the crystallization temperature of the mixture, to a finaltemperature greater than or equal to the melting point of the eutecticof the constituents of the said reaction mixture, so as progressively tocrystallize the adipic acid of the reaction mixture.
 9. Processaccording to claim 8, wherein the initial temperature is between 100° C.and 200° C. and the final temperature between 0° C. and 70° C. 10.Process according to claim 1, wherein the refining contains a secondphase, or draining phase, making it possible to separate at least a partof the catalyst within a draining fraction.
 11. Process according toclaim 1, wherein the refining contains a third phase, or sweating phase,consisting, by progressive heating of the deposited crystals, inrecovering a sweating fraction containing another part of the catalystand other constituents of the treated reaction mixture.
 12. Processaccording to claim 11, wherein the sweating phase is carried out byheating at a temperature between the final temperature of the drainingphase and 150° C.
 13. Process according to claim 1, wherein the durationof the refining cycle varies between 1 hour and 30 hour.
 14. Processaccording to claim 1, wherein the fraction obtained in the drainingphase is recycled to the hydroxycarbonylation reaction.
 15. Processaccording to claim 1, wherein the fractions obtained in the draining andsweating phases are recycled to the hydroxycarbonylation reaction. 16.The process according to claim 1, wherein at least 80% of the weight ofthe catalyst contained in the reaction mixture is separated by therefining operation.
 17. The process according to claim 11, wherein thesweating phase is carried out by heating at a temperature between 100°C. and 145° C.